I'm confused, are people really having this bad an experience in Flex? We're making a point as a guild (we're a large social guild) to do open Flex raiding on Friday nights, we took 25 people last week all ranging in gear from 49x to 540 with the average being about 520 and we wiped one time to Sha of Pride, for most people it was their first time seeing these bosses.
I know Pugs are always a wild card but frankly it was almost as easy as LFR, with the difference being pretty much that you can't actually stand in the fire on Flex, the damage and healing requirements were roughly the same, maybe about 20% higher.